Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

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Table 3.1: Panel test specimens. Lay-up type Core material Debond diameter (mm) No. of specimens 100 2 A H130 200 300 2 2 Intact 3 100 2 B H250 200 300 2 2 Intact 3 100 3 C PMI 51 IG 200 300 3 3 Intact 3 Each layer of DBLT-850 fabric contains approximately 835 g/m 2 glass reinforcement and each layer of DBL-800 has approximately 810 g/m 2 . Each face has in addition a 100 g/m 2 layer of chopped strand mat (CSM) placed against the core at the interface. Typical properties for the laminates are given in Table 3.2. Table 3.2: Face sheet material properties from experiments conducted on samples from the face sheet. Material property Type A/B Type C Elastic modulus, x-direction (GPa) 19.4 26.4 Elastic modulus, y-direction (GPa) 19.4 11.7 Elastic modulus, z-direction (GPa) 9.2 9.2 Poisson’s ratio xy 0.316 0.514 Poisson’s ratio xz 0.32 0.32 Poisson’s ratio yz 0.32 0.32 Shear modulus, xy (GPa) 7.4 7.4 Shear modulus, xz (GPa) 3.0 3.0 Shear modulus, yz (GPa) 3.0 3 Tensile strength (MPa) 294/313 490 Compression strength (MPa) 300/320 463 These in-plane properties are based on tests performed on similar laminates, but without a CSM layer. These laminates had a 53.8% fibre volume ratio, resulting in a thickness of 0.61 mm or 0.59 mm for each layer of DBLT-850 or DBL-800 reinforcement, respectively. The thicknesses per layer for the laminates in the tested panels were observed to be slightly higher than the calculated thicknesses. This appears to have been mainly due to the extra CSM layer. Burn-off tests performed on specimens taken from the face sheets indicated fibre volume contents between 51.5% and 55.3%, 42
the lowest values being for the Type C (triaxial DBL-800) laminates. The core materials are Divinycell PVC foams of type H130 and H250, and Rohacell PMI foam of type 51-IG. The properties for the core materials, taken from the manufacturers’ data sheets, are given in Table 3.3. Core type Nominal density (kg/m 3 ) Table 3.3: Material properties of the cores. Compressive modulus (MPa) 43 Shear modulus (MPa) Compressive strength (MPa) H130 130 170 50 3 H250 250 300 104 6.2 PMI 52.1 70 19 0.9 3.3 Characterisation of Face/Core Interface The interface fracture toughness characterisation of the foam cored sandwich specimens was performed using the Mixed Mode Bending (MMB) test rig and the MMB sandwich specimen (Quispitupa et al., 2009 and 2010), as shown in Figure 3.2. The MMB test rig was originally developed for mixed-mode fracture testing of monolithic composites (Reeder et al., 1990 and Ozdil et al., 2000) and has recently become an ASTM standard test method D6671-01. The MMB test rig allows adjustment of the mixed-mode ratio by changing the lever arm distance c as shown in Figure 3.2. Quispitupa et al. (2009) further developed the MMB test rig for fracture testing of sandwich structures. The standard MMB composite test specimen is a rectangular unidirectional beam specimen with a predefined delamination located at the midplane. In the MMB sandwich specimen the initial crack is located in the face/core interface at the top of the specimen, see Figure 3.2. The compliance of the MMB sandwich specimen is determined by (Quispitupa et al., 2009): where and P are the deflection of the loading point and the applied load, respectively, c is the lever arm distance, L the half-span length and is the load partitioning parameter at the left support (see Figure 3.2) given by 3 a 1 a 1 3 D2 k G f h f Gxzhc 3 3 (3.2) a 1 a 1 a 1 a 1 3 D k G h G h 3 D k G h 2 f f xz c 1 f f where the subscripts 1 and 2 refer to the face sheet and the core, respectively, a is the crack length, k is the shear correction factor, k=1.2, D2=D-B 2 /A, D1=1/(Efhf 3 /12), hf and hc are the face (3.1)
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Residual Strength and Fatigue Lifet
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Published in Denmark by Technical U
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This page is intentionally left bla
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method to accelerate the simulation
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Synopsis Sandwich kompositter er i
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Page 14 and 15: Contents Preface Executive Summary
Page 16 and 17: 5 Face/core Interface Fatigue Crack
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Page 20 and 21: H11 bimaterial constant H22 bimater
Page 24 and 25: These peculiar damage modes often r
Page 26 and 27: 1.2 Overview of the Thesis In this
Page 28 and 29: Figure 1.3: Fracture modes, from Be
Page 30 and 31: In Equations (1.5) and (1.6) H11, H
Page 32 and 33: Figure 1.6: Schematic illustration
Page 34 and 35: The compact tension specimen (CT) i
Page 36 and 37: A Figure 1.10: CSB, DCB, TSD, DCB-U
Page 38 and 39: Chapter 2 Buckling Driven Face/Core
Page 40 and 41: (DIC) measurement system (ARAMIS 2M
Page 42 and 43: corresponds to the onset of debond
Page 44 and 45: Figure 2.7: Crack kinking into the
Page 46 and 47: (2.2) where and for plane str
Page 48 and 49: A modified version of the tilted sa
Page 50 and 51: previous observations of crack path
Page 52 and 53: of contact elements (CONTACT173 and
Page 54 and 55: the debond opening initially increa
Page 56 and 57: Table 2.4: Instability loads determ
Page 58 and 59: G (J/m2) 600 400 200 0 H100 IMP=0.1
Page 62 and 63: Hayman (2007) has described a damag
Page 66 and 67: sheet and the core thickness, respe
Page 68 and 69: Load (N) 250 200 150 100 50 0 H130
Page 70 and 71: Table 3.4: Parameters in the face/c
Page 72 and 73: was used to monitor 3D surface disp
Page 74 and 75: arising due to the junction between
Page 76 and 77: (a) Debonded face sheet Figure 3.16
Page 78 and 79: Figure 3.19 shows the determined en
Page 80 and 81: H130 MMB H130 Panel H250 MMB Interf
Page 82 and 83: 3.6 Conclusion In this chapter the
Page 86 and 87: composite laminates under thermal c
Page 88 and 89: S S y( t ) y( t ) ( t ) 2 1 12 2
Page 90 and 91: listed in Table 4.1. The length and
Page 92 and 93: The strain energy release rate, G,
Page 94 and 95: high growth rate of G (see Figure 4
Page 96 and 97: 4.4 Face/Core Fatigue Crack Growth
Page 98 and 99: Debond 310 mm Symmetry B. C. a Figu
Page 100 and 101: B 2 1/ 2 ( S44 S55 S45) (4.17) wh
Page 102 and 103: 75), which illustrates possible ina
Page 104 and 105: Figure 4.18 (a) presents the deflec
Page 106 and 107: Debond radius (mm) 100 90 80 70 60
Page 108 and 109: using the cycle jump method, more t
Page 110 and 111: Chapter 5 Face/Core Interface Fatig
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H250 Specimen H100 Specimen H45 Spe
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Figure 5.5: Test setup. Initially,
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H100 Specimen Fibre bridging Figure
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propagation, the crack continues to
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Figure 5.14: Kinking of the crack i
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Crack length [mm] Crack length [mm]
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mode-mixity phase angle was chosen
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should be taken into account for a
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Figure 5.25: Kinking of the crack i
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log (da/dN) (mm/cycle) 10 log G (J/
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erroneous extrapolations in the tra
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compared to the 65% efficiency obta
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the case of uneven debond growth, t
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Load (kN) 2 1.5 1 0.5 0 Panel 1 Pan
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Figure 5.42: Zero and ninety degree
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G(J/m 2 ) 180 150 210 120 150 100 5
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110 q=qG=0.4 Test #1 100 Test #2 Te
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panels were determined for differen
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Chapter 6 Conclusion and Future Wor
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toughness using MMB fracture toughn
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For the specimens with H250 core th
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Development of testing methods for
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Bezazi A., Mahi A. E., Berthelot J.
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Kanny K. and Mahfuz H. (2005), Flex
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Ratcliffe J. and Cantwell W. J. (20
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Out-of-plane displacement (mm) 1 0.
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Out-of-plane displacement (mm) 3 2
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A.5 Out-of-plane deflection of Debo
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(a) Figure A.14: Out-of-plane defle
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(a) (b) Figure A.18: Out-of-plane d
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Load (kN) 250 200 150 100 50 250 30
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Displacement (mm) 4 3 2 1 0 8 9 (a)
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(a) (b) Figure B.11: Out-of-plane d
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(a) (b) Figure B.15: Out-of-plane d
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DTU Mechanical Engineering Section
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